The original design using binder clips served me well. But after a few iterations of that, I decided to make something a bit more fumble-free.
The spring is 1/4" x 1/2" x .035". Found bags of 5 at my local hardware store. I also use them for hotbed leveling. Screws are M3x5 flathead x 3 for mounting the motor. An M3x25 screw secures the arm through to the motor. A pair of M3x10 button head screws secure the top of the lever. The bowden tube is secured by threading a 4mm nut which is held in the lever by the top cap.
The bearing is a 608ZZ v-groove bearing. It seems to do a good job of keeping the filament on track. The guide and bowden tube are dead center to the bearing so that by itself helps too.